1. Field of the Invention
The present invention relates generally to read head sensors for magnetic heads, and more particularly to an improved sensor structure in which an antiferromagnetic pinning layer is removed from the central stack of sensor layers between the magnetic shields of a CPP sensor.
2. Description of the Prior Art
A hard disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk, where the magnetic head, or heads, read from or write data to concentric data tracks defined on surface of the disks. The goal in recent years is to increase the amount of data that can be stored on each hard disk. Increasing the a real data storage density of the disks can be accomplished by reducing the size of data bits, such that the number of bits per inch (bpi) on the data tracks on the disk can be increased. However, to read data from a disk with an increased bpi, it is also necessary to develop a sufficiently thin read gap structure within the read head of the magnetic head, such that unwanted magnetic field interference from adjacent data bits is substantially eliminated.
A read head typically includes a magnetoresistive (MR) spin valve sensor structure for reading the data from the disk of the hard disk drive. As is well known to those skilled in the art, such MR sensor structures include a plurality of thin film layers disposed between two magnetic shields that define the read gap. The thin film layers have particular magnetic properties, and are sensitive to the magnetic field of the data bits on the hard disk. Thus, thinner layers disposed between the two magnetic shields will create a thinner read gap, which will allow the read head to detect the smaller data bits that a higher bpi data track contains.
The thin film layers of a typical GMR spin valve sensor will include at least one antiferromagnetic (AFM) layer, at least one pinned magnetic layer, a spacer layer, at least one free magnetic layer and a magnetic biasing layer for the free magnetic layer. The magnetic biasing layer may require a second AFM layer to pin its magnetization in a desired direction. In operation the magnetic moment of the free layer is free to rotate laterally within the layer with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic field signals from data bits located on the rotating magnetic disk. The biasing layer stabilizes the free magnetic layer in its zero bias point position.
There are generally two ways to provide sense current to the read head. The older way is by supplying a current that runs longitudinally in the plane of the ABS from one side of the free magnetic layer to the other side. A more recent design is to supply the sense current perpendicularly to the plane (CPP) of the central layer stack; that is, between the magnetic shields. In such CPP head designs it is a practice in the prior art to pin the magnetization of the bias layer by using a layer of antiferromagnetic (AFM) material within the central layer stack, but this method can have disadvantages that result from the thickness of the AFM material, which is typically relatively large. This thickness of AFM material may be so great that it is a significant factor in the size of the read gap of the read heads. Therefore, there is an advantage to CPP read head sensors having a pinned bias layer that do not require that the AFM layer be disposed within the central layer stack between the magnetic shields.